1. Field of the Invention
The present invention is generally directed to a fixing device for fixing a toner image to a recording medium, and also directed to an image forming apparatus.
2. Description of the Related Art
Among fixing devices used in image forming apparatuses, one known type of such applies heat and pressure to paper, on the surface of which an unfixed toner image is carried, by holding, the paper between a heating roller and a pressure roller while conveying the paper, to thereby fix the toner image onto the paper.
At a stage previous to the pressure roller, a heating plate having multiple heaters inside is provided, and the heating plate applies heat to the paper. This application of heat by the heating plate is ancillary to the application of heat and pressure by the heating roller and the pressure roller to the paper which is held between these rollers and conveyed. In general, image forming apparatuses that perform high speed printing or support long continuous paper (web) require increased heat capacity for fixing toner images. Applying heat to paper supplementarily by the heating plate facilitates reducing an increase in the fixing temperature.
Heating paper by the heating plate allows the temperature of the heating roller to be reduced; however, if paper is laid on the heating plate for more than a fixed period of time when a printing job is stopped, the paper is heated more than necessary, which sometimes results in paper contraction and/or damage.
In order to solve such a problem, a technology has been proposed that detaches the paper from the heating plate using a pin, a wire or the like (see Patent Document 1, for example).
In another known technology, when conveyance of printing paper is stopped in a second printer used for tandem duplex printing, air is sent from the printing paper side in order to prevent an increase in temperature of an area between detached paper and the heating plate, prevent the paper from being deformed by heat and reduce quality loss in printing of the back side of the paper (see Patent Document 2, for example).    [Patent Document 1] Japanese Laid-open Patent Application Publication No. H10-123864    [Patent Document 2] Japanese Laid-open Patent Application Publication No. 2006-215361
However, simply detaching the paper from the heating plate according to the technology of Patent Document 1 is not sufficient and paper damage/contraction is sometimes caused since the paper is heated by radiant heat from the heating plate. Furthermore, even when a mechanism for sending air from the printing paper side is provided, as in the case of Patent Document 2, paper damage/contraction may still be caused.